Electrotherapeutic oscillator



Get. 27, 1953 c, HOWARD 2,656,839

ELECTROTHERAPEUTIC OSCILLATOR Filed Feb. 14, 1950 5 Sheets-Sheet l 3nventor CLARENCE B. HOWARD attorneghi Oct. 27, 1953 c, HOWARD ELECTROTHERAPEUTIC OSCILLATOR 3 SheetsSheet 2 Filed Feb 14, 1950 ZSnnentor CLARENCE B. HOWARD *JQQDM 538 w attorneys Oct. 27, 1953 c. B. HOWARD 2,656,839

ELECTROTHERAPEIUTIC OSCILLATOR Filed Feb. 14, 1950 3 Sheets-Sheet 3 FIE 5 :mventor CLARENCE B. HOWARD W4 SW (1 ttornegs Patented Oct. 27, 1953 UNITED STATES PATENT OFFICE 2,656,839. ELECTROTHER-APEUTIC. OSCILLATOR Clarence B. Howard, oaklana'caliri Application February 14, 1950, Serial No. 144,083

4, Claims.

invention relates tooelectric oscillators, and particularly to oscillators. which deliver multiple frequencies for therapeutic purposes;

In therapeutic treatments by the diathermic method, i; e.,. by subjecting the body of the patientto high frequency magnetic or electric fields which induce inthe body electric currents of corresponding frequency, thuscausing a rise in local' body temperature and various other efiecta. there is parts respond more powerfully to certain frequencies than toothers and further evidence that it is possible that treatment with complex waveforms, i. e-., simultaneous treatment by multiple frequencies, is more: effective than treatment by fields of any single frequency; One of the objectsofthis invention. is therefore to provide oscillators and oscillator circuits for generating such multiple frequencies;

One oi the difficulties of giving treatments of the character described .has been that with conventional types of electronic oscillators it has proved difilcult to develop fields of suflicient strength to produce the desired therapeutic re.- sults without radiating large amounts of high frequency power which will cause radio interference over large areas on the one hand, or, on the other, so changing the tuning of the oscillator system by introducing the patient into the field or by shifting his position in. such field that the amount and intensity of the treatment are. extremely difiicult to control. Other objects of this invention are, therefore,v to provide a means of. producing a powerful local field which falls on very rapidly in intensity with distance the: treatment device, to provide such a field which is controllable in intensity, to provide a fi'ield wherein the frequencies developed remain substantially constant whether or nota patient is introduced therein, and to provide a means for producing the eifects described with simple and economical apparatus.

Considered from one aspectthe instant invention comprises the use of an oscillating and fieldgenerating element in the form. of a quasi-spiral inductor which isprovided with dead end branch conductors connected to the spiral at intervals and lying substantially in the same surface therewith and between the turns thereof. As will be developed more fully hereinafter such an inductor has a multiplicity of modes of oscillation, all of which can be excited simultaneously and all of which will set up powerful. fields in the neighborhood of the oscillating circuit but which fall off in. intensity very rapidly both with I evidence that different body i from i gaps in the preceding rings,

distance and with: changes in angle with. respect to theorientation of the inductor; From another point of view the invention comprises the use: of a plurality of inductors of the type described, oneof which comprises the main power circuit of the oscillator, the other of which lies between the inductor and; the patient to: be treated and is tunablein such manner as to regulate the intensity of the field which reaches the patient.

Phe foregoing will be more. clearly understood by reference to the following detailed description of a preferred embodiment of. the invention, considered in. connection with the accompanying drawings wherein:

Fig; 1 is an elevation ofv the oscillating system used in the preferred. form ofthe invention;

Fig. 2 is a plan view of the system illustrated in Fig. 1;

Fig. 3 is a. schematic diagram of the circuits employed in the inductor array illustrated in Fig. 1;.

Fig. 4 is a similar schematic diagram showing another type of oscillating circuit in which such inductors. may be employed;

Fig. 5- is a diagrammatic. representation of. a modified form of inductor configuration; and.

Fig. 6 is a diagram of field. strength with relation to the coil system. illustrated in Fig. 1.

Considering first. Figs 2 of the drawing, the reference character I designates generally an inductor of the type which is incorporated in and, in most cases, constitutes the oscillating circuits employed in the device of this invention. The actual construction of. inductors of this character may be accomplished in a. number of ways, but in; the: preferred form illustrated the inductor; comprises a. plurality of substantially concentric rings of conductive materials" designated' by the referencecharacters 21'to T inclusive, each ring being, however, incomplete in that it includes a narrow gap 9. The rings are mounted substantially concentrically and in the same plane, and in the case illustrated are formed of conductive rod or wire of low resistance; e. g.,. copper rod of a diameter of about 1% of an inch silver plated to give high surface conductivity (and hence overall conductivity) at the frequencies employed, together with resistance to corrosion which would raise the electrical resistance of the device. In the example shown the gaps in the successive rings are displaced by approximately 180" ofiarc from the but the. angle of disthis path being traced from the end of the inner conductor 2 to substantially its midpoint, thence across the bridging connector II to the end of conductor 3, and on counter-clockwise around the conductor to substantially its midpoint, thence across bridging conductor I3 to the end of conductor and so forth, always in a counterclockwise direction, to the outer ring, which, of course, has no midpoint connection as there is no succeeding ring to which it could be connected. This arrangement leaves, at each bridging connection II through I3, a dead end conductor which lies intermediate the turns of the spiral path.

An inductor of this form possesses a large number of modes of oscillation. One of modes, which can be considered as the primary or fundamental mode, is at a frequency which is etermined by the inductance of the complete path, taken in connection with the distributed capacity of the device and the capacitances, either actual or virtual, which may be connected across its ends and to ground, as is the case with any inductive oscillating circuit of ordinary type. Many other modes of oscillation exist,

owing to the multiplicity of dead end conneci tions and the paths which can be traced with respect thereto. One group of such paths may be considered to exist between the two ends of any turn. Another mode may exist from the inner end of the quasi-spiral coil to the free end of any one of the dead end connections. Other the outer end of the rings to any of the free ends of any of the connections. Still other frequencies may exist because of conplings and resonances between the paths that have already been mentioned, or by virtue of similar couplings to an adjacent oscillating circuit of the same type.

In the present instance each of the rings form ing the inductor is provided at positions 90 7 from the gap in the ring with a screw stud 2| whereby it may be secured to a transverse insulating mounting member 23 as is shown in Fig. 1.

In the form of tion three elements of the general type shown in Fig. 2 are mounted in adjacent parallel planes. The upper element I, mounted on the supporting bar 23, comprises six equally spaced rings, the inner of which is approximately four inches and the outer nine inches, in outside diameter. A second inductor, I, is slightly larger, having one additional turn carried on its support bar 23'. A third inductor, I", has the same dimensions as that first described and is mounted on the insulating support bar 23". All three support bars are mounted in fixed spacial relation on a pair of vertical struts 25, and are locked in place by nuts and washers threaded onto these struts. Due to the rather large diameter of the inductors and to the relatively small spacing between them the coefiicients of couplings are quite high, approaching unity. The struts 25 are supported by a transverse crossbar 2'! and are conveniently mounted with these the device chosen for illustrathe plane of the upper coil closely adjacent and parallel to the plane of a treatment table, the position of which is indicated by the dot-dash line 23. Since the actual method of application is no part of this invention and since the patient may be apposed to the oscillating circuit in other ways than by placing such patient upon a treatment table, such table is not shown in detail, its plane being merely indicated for the purpose of showing the most effective position of the device with reference to a patient to be treated, and not by way of limitation.

The assembly of Fig. 1 is designed for connection into the circuit schematically illustrated in Fig. 3. As is there shown the outer end of the inductor l connects with the plate 3I of a triode 33, its inner end being connected to a conventional power supply 35, the negative end of which connects to ground. The cathode 31 of the tube 33 is also connected to ground through a biasing resistor 39. The outer end of coil I" connects to the grid ll of tube 33 and its inner end to ground. Coils I' and I" therefore constitute, respectively, the plate and grid coils of a conventional tickler oscillator. In the device illustrated the tube 33 is a high-mu power tricde with a nominal output power of I50 watts, the grid resistor 39 has a value of about 1500 ohms and the power supply is adjustable with a maximum output of 500 milliamperes at 2000 volts. In this specific instance a bleeder 43 of 100,000 ohms resistance is connected across the power supply to prevent undue surges of voltage when the device is not operating under load or during transient conditions.

Control of the field strength applied to the patient is secured through the inductor I, the inner end of which is connected to ground through a small variable condenser 45. The outer end of inductor I is left free. This particular inductor therefore might be considered as an antenna, since its connection greatly resembles that of such a structure. To some extent it exercises an antenna function; the load upon the tube 33 can be adjusted through wide limits by varying the tuning of the condenser 45, which, in the case illustrated, consists of a pair of aluminum plates 41 and 41', one of which is mounted on an insulated strut 49 in a fixed position, the other being adjustable by means of an axial screw 5| threaded through a fitting 53 carried by a strut 54 on a bracket 55. The adjustable plate 41 is grounded.

The power drawn by the tube 33 can be quite accurately controlled by varying the tuning of the condenser 45. Owing to the fact that it is generating many different frequencies and the actual operating efficiency of the circuit varies widely with respect to these frequencies, its overall efficiency is not high and it is found that the tube overheats if an attempt be made to use its full rated output. The output mentioned is, however, sufficient to raise the local temperatures of the patients to the desired degree, and the actual use of the device is not such as to make the utilization of the tube itself at maximum efficiency of primary importance. Where greater power has been required I have utilized two tubes of similar characteristics in parallel and additional tubes can ,be added if desired. Since similar expedients are frequently adopted in analagous arts it is not considered necessary to illustrate multiplications of this character.

Although for reasons of certainty of operation, convenience, and stability of adjustment I prefer 8 tousethecircuit illustrated in, Fig. 3, almost any" other of the conventional oscillating circuits utilized in electronic practice may be employed. Fig. 4 is a. schematic illustration of the invention employing an oscillating; circuit: of the wellknown Heising type, in which the inductor V is used in common for both plate and grid; In this modification the outer terminal of the coil is connected to the plate SI of tube 33' as before; the inner end of coil I connects to grid II through a blocking condenser 55, grid bias being supplied through a leak resistance 51. The other parts of the circuit are as before, the coil I connecting to ground through a tuning condenser 45 in precisely the same manner as in the circuit previously described. Practically any other con ventional type of oscillating circuit may be used.

It might be expected that the coil I would act as a shield between the oscillator and the patient, and prevent any substantial field from reaching the latter. That this is not the case is indicated by the field diagram shown in Fig. 5.

In Figure 5 curves 6B and 6| represent loci of equal field strength in relation to the coil I positioned as shown in the figure. Curve 60 represents measurements made at the lowest or fundamental frequency of oscillation to which the field strength measuring equipment could be tuned to give a peak measurement. Curve 6| shows a similar curve with the field strength measuring equipment tuned to the highest recognizable peak, the scales of both of the two curves being the same. It will be noted that the forms of the curves for the high and low frequency are quite different, and it has been found that both fields approach zero below the plane of the coil I, but this is unimportant since it is in the area above the coil that the patient is placed.

Nothing has been said thus far about the nature of the fields produced, and the probability is that they are of mixed character but that the major component is an inductive rather than a radiated field, this inference being drawn owing to the great rapidity with which both high and low frequency fields drop off in intensity as the distance from the coil I is increased. Neither an inverse square nor an inverse fourth-power law is followed exactly, but the latter is approached more closely than the first. In any event it has been found that oscillators of this type create no serious interference with communications, and much more powerful fields can be used without creating such interference than is possible with ordinary diathermic equipment. This is the more remarkable when the nature of the waveforms 57 generated is considered; a wave meter used adjacent the device will detect a very large number of peaks, none of which, however, appears to be dominant and material amounts of energy can be detected between such peaks.

The effect of the coil I appears to be to absorb power from the oscillating circuit and reem it such power to the patient. Therefore, while it does not act as a shield in the ordinary sense of preventing flow of energy past it, it does prevent changes in the position of the patient and consequent changes in capacity from being reflected into the oscillator and changing its frequency. Best performance is obtained by setting the condenser 45 so that the oscillator tube does not overload at maximum plate voltage and leaving it so set. The power delivered to the patient can then be controlled Without material change in frequency by varying the plate potential on the tube.

Experimentation with the apparatus has shown that the tuningfl'lf so it may be called, of the dead end conductorsin the oscillating circurt isnot critical and that-it appears to be unnecessary to preserve extreme accuracy of measurement as between coupled inductors of this-type. This situation might be different if an attempt were made to hold the higher frequency components of the gene-rated oscillations to any exact value, but thus far there appears to be no for doing this since the high frequency pears are of sumcienuy minor value and are so closely spaced that no serious error is introduced inconsidering them asa substantially continuous band. No difiiculty has been experienced in generating multi-frequency oscillations of this character so long as the main circuits controlling the fundamental frequency are within the range wherein oscillation at this fundamental might be expected; in other words, the criteria used in designing a single-frequency oscillator of any type which may be desired may be used in designing the inductors and satisfactory oscillation will result. Well known factors may therefore be employed to determine the fundamental frequency of oscillation, and the desired multiple frequencies of higher value will follow without further consideration. The device may therefore be designed for operation in almost any frequency range, by suitable change in dimension, and the dimensions given in the case chosen for illustration are therefore purely of illustrative character.

As should be evident to those skilled in the art it is the electrical and not the mechanical form of the inductors which is important, and the split ring construction which has been described is merely one convenient Way of making the coils. The main, quasi-spiral circuit may be formed as an actual spiral, with dead-end branch conductors soldered or welded thereto in a manner more comparable to that illustrated in the diagrammatic showings of Figs. 3 and 4 than to the structural drawing shown in Fig. 2. The spirals themselves may depart quite widely from an overall circular form. If the ring structure is used the rings may be elliptical rather than circular, or a square-type coil may be constructed of the form diagrammatically illustrated in Fig. 5. Another possible modification is to cut or punch the inductors out of a single sheet of metal, and still another is to cast them. All such methods of construction are considered to fall within the scope of my invention. Furthermore, while I have found the method of controlling field strength by mean of the free ended antenna coil of especial value where multiple-frequency treatment currents are employed, the same expedient is effective with conventional spiral inductors.

I claim:

1. In an oscillation generator, a multi-frequency oscillating circuit comprising a plurality of substantially concentric conductive rings each having a gap therein, the gaps in successive rings being angularly displaced with respect to each other, and bridging connections between each two successive rings, said connections extending from a point adjacent the gap of one rin to a point intermediate the ends forming the gap of the next ring to provide a quasi-spiral current path through said rings with a plurality of deadend conductors branching off between turns of said spiral.

2. A multi-frequency oscillating circuit in accordance with claim 1 wherein the gaps in suc- 7 cessive rings are displaced with respect to each other by substantially 180.

3. In an oscillation generator, an oscillating circuit comprising a conducting element formed to provide a substantially spiral main current path, and subsidiary dead-ended branch paths each connected at one end to a difierent point on said main path and disposed between the turns thereof.

4. An oscillating circuit in accordance with claim 3 wherein said dead-ended conductors are each of difierent length.

CLARENCE B. HOWARD.

References Cited in the file of this patent UNITED STATES PATENTS Number 

